The present invention relates to an improved electrical energy storage system, and more particularly the invention relates to an improved metal halogen battery construction which includes a combustion arrester to prevent the possibility of harmful reactions between hydrogen and halogen gases which are present in the system, for example, to prevent self propagating reactions between hydrogen and chlorine gases which may be present in the system.
The electrical energy storage system of the type referred to herein (e.g., a zinc-chlorine battery system) utilizes a halogen hydrate as the source of a halogen component for reduction at a normally positive electrode, and an oxidizable metal adapted to become oxidized at a normally negative electrode during the normal discharge of the storage system. An aqueous electrolyte is employed for replenishing the supply of the halogen component as it becomes reduced at the positive electrode. The electrolyte contains the dissolved ions of the oxidized metal and the reduced halogen and is circulated between the electrode area and a storage area containing halogen hydrate which progressively decomposes during a normal discharge of the electrical energy system, liberating additional elemental halogen to be consumed at the positive electrode, Electrical energy storage systems or battery systems of this type are described in prior patents owned by the same assignee as the present invention, such as U.S. Pat. Nos. 3,713,888, 3,993,502, 4,001,036, and 4,146,680. Such systems are also described in published reports prepared by the assignee herein, such as EPRI Report EM-1051 (Parts 1-3) dated April 1979 published by the Electric Power Research Institute. The specific teachings of the aforementioned U.S. patents and the EPRI Report are incorporated herein by reference.
During the cycling of a metal halogen battery, such as for example a zinc-chlorine battery, small amounts of hydrogen are generated at the zinc electrode. The hydrogen gas is normally recombined with chlorine gas to form hydrogen chloride by means of chemical reaction (see page 15-11 of EPRI Report EM-1051). At low hydrogen concentrations (e.g., about 1-5%), the reaction proceeds smoothly. However, under certain conditions hydrogen gas may accumulate in the battery system and this can be very troublesome because, at higher hydrogen concentrations (e.g., about 10% or greater), the reaction between hydrogen and chlorine becomes self propagating, and thus there may be generated pressure fronts capable of breaking or rupturing the battery container. Moreover, previous techniques for carrying out the reaction (such as shown at page 15-11 of EPRI Report EM-1051) are not satisfactory from the standpoint that at higher hydrogen concentrations or build-ups, no provision was known which would adequately inhibit the hydrogen-chloride reaction from being rapidly propagated throughout the battery container, thus possibly leading to fracture or rupture thereof. This is a critical problem particularly with respect to the usage of such battery systems in electric vehicle applications.
Accordingly, one object of the present invention is to provide a novel battery construction technique wherein the reaction of hydrogen and halogen gases generated in the battery system can be maintained under carefully controlled conditions to avoid any possible rupture or fracture of the battery container.
Another object of the present invention is to provide a metal halogen battery system which includes a novel combustion arrester means to prevent the self propagation of hydrogen reactions, such as hydrogen-chlorine reactions.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.